Whistles are widely used as means for transmitting various pieces of information to a person or an animal far away quickly, inexpensively, and simply using the breath of a human without any electrical or mechanical complex mechanism. As is clear from the purpose thereof, the most important functions required for whistles are to blow discriminative tone which can be distinguished from other sounds and to be blown at a sound volume as large as possible.
It is well known that the whistles have the same blow principle as those of wind instruments. That is, the frequency (tone) of whistle sound is set based on the shape and the size of a resonant chamber, and the sound volume (magnitude of sound) is set based on an amount of air (airflow) to be blown in. In contrast, whistles as commercial products have advancement in the manufacturing method thereof based on the advancement of materials and machines, but have no large advancement in the principle ever since the original model was made in late 1800s. The structure of whistles can be classified into two kinds.
First one is that a mechanical oscillator like a cork is put in a resonant chamber formed in a short-cylindrical shape, and beat sound is generated by the turning motion of the oscillator due to exhaled breath and resonance, and this structure is the most popular structure because blowing is easy. Hereinafter, this is called an oscillator whistle.
Another is one which does not use a mechanical oscillator, and is configured by a plurality of tiny resonant rooms (hereinafter, a collection of plural tiny resonant rooms is called a composite resonant room) each formed in a single or plural long cylindrical shapes, and orifices. This structure requires a certain level of proficiency to blow, and is mainly used for sport referees. This structure is called a non-oscillator whistle.
Next, an explanation will be given of the present situation and the problem in detail relating to the foregoing two requisite performances (discriminative tone and sound volume). First, regarding the tone, because the practical shape of a resonant room and the size thereof are limited, the blown frequency is thus limited. More specifically, the frequency of an oscillator whistle is 2.5 to 3.5 KHz, and that of a non-oscillator whistle is 3.5 to 4.5 KHz. As is clear from those numerical data, the whistle sound of the oscillator whistles is low, and is called a “low-pitched sound type” in some cases. In contrast, the whistle sound of the non-oscillator type is high, and is called a “high-pitched sound type” in some cases, and both whistles are used selectively depending on the kinds of sporting events and the use environments.
Whistles used ordinary have a size in a mouthpiece end (air-supply end) formed by the width (15 to 24) mm multiplied by the height (6 to 9) mm and the length without a strap hole (42 to 55) mm. Accordingly, the range of the foregoing frequency further becomes narrow, it is difficult to distinguish tones among the same whistles, so that it brings about various problems. A noticeable example of such problems is that a plurality of same or different sporting events are simultaneously carried out at the same site. For example, in the case of basketball, games are simultaneously carried out at two courts or three courts in the same floor. In basketball games, it is often that whistles are blown to judge fouls properly, so that it is possible to hear the whistle sounds at an adjoining court, and the whistle sounds may be misrecognized, and often resulting in interruption of a game. Therefore, it is necessary for players to always pay attention whether or not a whistle sound is in their court, resulting in interruption of concentration to the game. Moreover, misrecognition may cause a trouble, and the game itself may become in a tangle. The same is true of other indoor sports, such as valley ball and a hand ball.
There is only one solution so far to use whistles having different tones (blown frequencies) in order to overcome the foregoing problem. Accordingly, referees are required to have different kinds of and a plurality of whistles, and it is confirmed in a meeting prior to a game that whistles having similar tones will not be used. In practice, however, it is not always true that a referee has a sufficient number of whistles for selection of tones, so that the foregoing problem remains unsolved yet.
So far, there are several proposes as techniques of realizing discriminative tone. The most popular technique is to utilize beat sound. Typical examples of such technique can be seen in U.S. Pat. No. 5,086,726 or U.S. Pat. No. 4,821,670. Both are non-oscillator whistles having three tiny resonant chambers with different lengths, i.e., a composite resonant chamber. The former has the three tiny resonant chambers each formed in a rectangular shape with a different length and arranged in the horizontal direction, while the latter has the two tiny resonant chambers among the three tiny resonant chambers, formed in a long-cylindrical shape with different lengths, and arranged at both sides of a top face, and also has the remaining one arranged at the center of the bottom face. Both whistles have the tiny resonant chamber with a length of 16 mm to 25 mm. According to both whistles, blown air flows through an air feeding tube commonly communicated with individual tiny resonant chambers (hereinafter, common air feeding tube), flows through individual air feeding tubes, and is fed in individual tiny resonant chambers, thereby generating resonance. The reason why the common air feeding tube is long (9 to 10 mm) is to suppress any nonuniform feeding of air into individual resonant chambers. Each resonance has a slightly different frequency, so that beat sound is generated which is well known conventionally. However, because individual tiny resonant chambers are not independent from one another, it is not possible to blow the resonant chambers individually, and the three tiny chambers work together as a single composite resonant chamber, resulting in a function as a single whistle. Accordingly, there is generated beat sound, but the tone thereof is fixed and single one, and it is not possible to blow the whistle while changing the tone. Therefore, in comparison with non-oscillator types having no beat sound, the tone differs, but there is no large difference in tones among whistles having beat sound because of the similar lengths of tiny resonant chambers.
Another interesting proposal is disclosed in Japanese Utility Model Application KOKAI Publication No. S60-49598. This propose utilizes the principle of open tube/close tube of wind instruments which is well known conventionally, and the resonant frequency is changed by forming an opening in a part of the wall of the resonant chamber in addition to an orifice. Furthermore, according to this disclosure, in addition to the foregoing propose, there is another propose that two resonant chambers having different lengths and air feeding tubes connected thereto respectively are arranged symmetrically in the horizontal direction. However, it is difficult to individually blow each of the two air feeding tubes arranged in the horizontal direction from the standpoint of a structure that the mouth cavity of a human is long in the horizontal direction, so that there is a problem that it is not possible to separately blow two different whistle sounds using a single whistle.
Moreover, forming an air exhaust port in addition to an orifice produces air leak, so that it is not possible for a person having a small breathing capacity, such as a child or an elder person to blow the whistle because he/she becomes hard to breathe. Unexamined Japanese Patent Application KOKAI Publication No. H07-64562 discloses a similar propose to the foregoing one, but the same is true in regard to this problem.
Conversely, regarding the sound volume, there is no whistle so far which can generate remarkably large sound. This is because the blow principle is same and the size is limited within a narrow range, so that it is difficult to find a new concept, and as far as it stands, an air feeding amount is increased or decreased as needed. The typical area of air feeding opening of the conventional whistles is 38 to 45 mm2 regardless of the oscillator type and the non-oscillator type. This is a size set with a view to enable most people including females and children to blow the whistle without becoming hard to breathe.
The sound volume of whistle sound of whistles is proportional to an air feeding amount per unit time (V), and the stronger a whistle is blown, the more the air feeding amount per unit time increases, resulting in increasing of the sound volume. Conversely, the breathing capacity of a man (L) is limited, so that it is not possible to keep blowing without limitation, and a whistling continuous time (T) is inversely proportional to the air feeding amount per unit time. That is, a relational expression that L=V×T is concluded.
As a specific example, in the case of an adult male, the average breathing capacity is 4000 cc, when the same male blow a typical oscillator whistle most strongly, i.e., the continuous time of the maximum sound volume is about 7 seconds, and as a result, the air feeding amount per unit time at the maximum sound volume (maximum air feeding amount per unit time) becomes 571 cc/sec. As is clear from this result, there is a close relation between the maximum sound volume and the maximum air feeding amount per unit time.
If a whistling person remains same, the maximum air feeding amount per unit time is set based on the size of an air feeding opening, the size, shape, and length of an air feeding tube, and the size of an orifice. According to conventional whistles, however, because those are all fixed, the maximum air feeding amount per unit time is also fixed and cannot be changed. That is, the maximum sound volume is thus fixed, and it is not possible to blow a whistle with a sound volume louder than the fixed maximum sound volume.
The only specific solution so far which can generate large sound and which is commercially available is a whistle having an increased whole size thereof, but females and children having little breathing capacity may have difficulty to breathe, so that not all people can use such a whistle, and it is not practical solution.
One of another reason why the sound volume is insufficient is that the orifices of conventional whistles are all opened upwardly (toward the top face direction). Because a listener is positioned in the front direction in most cases, whistle sound is once directed upwardly, and sound waves which reflect a ceiling or a wall reaches such a listener. As is conventionally well known, the sound volume is inversely proportional to the square of distance, so that reaching sound waves are unnecessarily attenuated.
Furthermore, because reflected wave has a longer propagation distance, a time until the wave reaches becomes long. As an example, the speed of sound propagating in air is m/sec, so that when a reflective reaching distance is m, it takes about seconds, and this is normegligible for a sport referee who uses a whistle and needs an instant judgment.